Integrated Fixed-Film Activated Sludge

Challenge

The city’s wastewater treatment plant experiences significant industrial loads. This plant was originally constructed as a two-stage trickling filter plant. In the mid-1990s a parallel activated sludge system was added to increase the plant’s organic treatment capacity. In 2004, the city needed to increase the plant’s overall treatment capacity to allow sufficient capacity for industrial loadings and growth. The challenge was to develop options for secondary treatment that would optimize the existing treatment facilities to increase the plant’s capacity.

Solution

Several secondary treatment technologies were investigated including upgrading trickling filters, the trickling filters/solids contact process, and a new “innovative” technology of trickling filters followed by Integrated Fixed-Film Activated Sludge (IFAS). IFAS is a relatively new technology that has limited experience in the United States. FOX thoroughly researched the technology and after evaluating all options, FOX and the city decided that upgrading the existing aeration basins to an IFAS system was the most beneficial option for increasing plant capacity.Solution

The IFAS media allows for additional biomass to treat higher loads in the same aeration basin footprint. The IFAS media and aeration equipment were installed in the aeration basins. A new high efficiency single-stage centrifugal blower was installed as well. A new 30 mgd pump station was installed with vertical turbine pumps to pump trickling filter effluent to the IFAS basins.

One of the other major improvements was the final clarifier modifications including an energy dissipating inlet (EDI) device, a larger flocculator feed well, and piping modifications to allow more flexibility. The two-sided weirs on inboard launders were also replaced with a new single baffle and weir on a new effluent trough designed to provide better clarifier currents and less solids carryover. A side-by-side comparison of this improved clarifier with a previously installed clarifier modification indicates a marked improvement in performance. The clarifiers also required dewatering operations during construction and maintenance because of the influence of the Missouri River groundwater levels.

Outcome

The project has been operational since June 2007. Throughout the planning and design phases FOX and city staff held more than seven formally organized meetings to brainstorm, review various stages of facility planning and design, and address operational concerns. The city has received a project that meets their needs based on their input. The innovative design has saved the city more than $1 million in capital costs.

“FOX always approaches the task with an open mind, and works with City staff to understand the City’s needs and budgetary limits.”

“FOX also has demonstrated a real ability to retrofit the alternatives into existing facilities which in itself is a challenge well beyond designing a totally new system.”

Ed Jankowski, P.E., Project Manager-Engineering Division

RECOGNITION

The application of the IFAS technology at Council Bluffs for new or existing wastewater treatment facilities provides an advanced technology for use by other engineers to reduce costs and provide better operations. This application was brought to use in Iowa from technology developed and manufactured in Europe. This not only provides for up close examination and testing, but also presents an additional source for future enhancements. The IFAS equipment is suitable for installation in existing basins and would reduce costs of additional plant expansions, especially as nutrient removal standards become more common in Iowa. This technology can be directly applied in existing basins to achieve increased treatment levels.

In addition to the evaluation, testing, and modeling performed to design this project, there were other design enhancements that could be beneficial to future projects. As mentioned in the previous section, additional testing for snail propagation within the IFAS media was performed and can be applied for future projects. FOX has worked with City operations staff during the startup and operation to monitor performance parameters and adjust operating parameters to observe changes in performance based on these modifications.

One of the concerns with the fixed media IFAS projects is that it is difficult to verify the amount of biomass on the media. Well-established procedures for measuring suspended activated sludge quantities have been established to allow operators to make process adjustments. However, similar methods of biomass measurement on fixed media have not been established. As part of this project, FOX engineers required smaller media sample “coupons” to be provided and installed in the basins so that the biomass could be measured in the future. These coupons can be dried and weighed to determine the mass of bio-organisms present for treatment.

This is the first known example of attempting to measure this biomass. Other attempts at biomass measurement were purely theoretical calculations based on treatment performance. The photo above shows one of these coupons after pulling it from the basin to view the biomass growth. This full-scale operating data, never before collected, will provide valuable information for future designs.